1. Field of the Invention
The present invention relates to woven membranes.
2. Related Art
Hollow fibers are converted into gas separation membrane modules in bundle forming wherein the hollow fibers are either placed parallel to a center core or wound around the core tube at an angle to the axis of the core tube. This type of membrane module manufacturing includes multiple steps performed by multiple machines that can be complicated, time-consuming and which present multiple opportunities for defects.
Some have instead proposed the formation of gas separation membrane modules by weaving the weft hollow fibers with warp threads on a loom followed by winding the woven fabric around a center core.
U.S. Pat. No. 5,598,874 disclosed such a woven gas separation membrane module. Two different warp threads were used: one in the central active region in between the two tubesheets and another in the selvage regions at both ends of the fabric. In particular, it proposed using a non-wettable or low-wettability synthetic thread (such as polytetrafluoroethylene or silicone rubber) in the selvage region in order to prevent wicking of the potting composition (that is later cured to form the tubesheet) up the bundle fibers and into the section of the fibers intended for the active region. However, such a use of a non-wettable or low-wettability thread is a double-edged sword. The same properties that prevent wicking of the potting composition will also result in a lower degree of coverage of the outer fiber surface by the potting material. In the finished tubesheet (after curing of the potting material), this lack of wetting leads to the presence of voids in between the outer surface of the hollow fiber partially wrapped with low-wettability warp threads and the adjacent tubesheet material. The voids in such a void-ridden tubesheet could act as stress concentrators in the tubesheet when the tubesheet is subjected to the high pressures typically experienced in gas separation processes. On the other hand, if a wettable thread was instead used, wicking of the potting material into the active region would no longer be prevented.
Thus, it is an object of the invention to provide a woven gas separation membrane module that does not experience the relatively weaker strength that would be expected in the void-ridden tubesheet resulting from the process proposed by U.S. Pat. No. 5,598,874. It is another object of the invention to provide a woven gas separation membrane module that avoids the problem of potting material wicking into the section of the fibers intended for the active region.